CN1124243A - Preparation of monochloro acetic acid - Google Patents
Preparation of monochloro acetic acid Download PDFInfo
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- CN1124243A CN1124243A CN 94112764 CN94112764A CN1124243A CN 1124243 A CN1124243 A CN 1124243A CN 94112764 CN94112764 CN 94112764 CN 94112764 A CN94112764 A CN 94112764A CN 1124243 A CN1124243 A CN 1124243A
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Abstract
The present invention relates to preparing monochloro-acetic acid (MCHES) through chlorination of acetic acid. After chlorination of acetic acid a kind of coarse MCHES is produced, through crystallization and centrifugalization, the MCHES is separated out from said coarse MCHES. The focal point of the present invention lies in that a kind of catalytic hydrogenolysis has been conducted before the step of crystallization.
Description
The invention belongs to the improvement of (MCHES) monochloroacetic acid process and can be applied to chemical industry.
MCHES is a valuable product for preparing hydroxymethyl cellulose, various pesticides and medicines.
Indirect hydration of monochloroacetic acid with trichloroethylene
The most closely related methods to be applied for the preparation of monochloroacetic acid include the continuous catalyzed liquid phase acetic acid (ES) chlorination and the isolation of monochloroacetic acid by means of crystallization and subsequent centrifugation. The liquid phase (mother liquor) separated from the crystals is returned to the chlorination stage (2).
In the known process, acetic acid is chlorinated using acetic anhydride as catalyst. The reactions carried out in the process can be represented as follows:
An important by-product is dichloroacetic acid (DCHES), which is formed upon chlorination of monochloroacetyl chloride:
the continuous chlorination of acetic acid is carried out in a final product medium comprising 75% by weight of MCHES (monochloroacetic acid), 18% by weight of acetic acid and 7% by weight of dichloroacetic acid at 100 ℃ and 120 ℃.
The chlorinated product is sent to the crystallization stage at 50 ℃. The product is cooled to 20-25 ℃ for crystallization. As a result, a suspension of MCHES crystals in a mixture of acetic acid and dichloroacetic acid is formed.
The suspension is then separated, for example by centrifugation. The solid phase is the commercial product and the liquid phase is sent to chlorination.
FIG. 1 shows a flow diagram of a known monochloroacetic acid process.
As can be seen from the description and the flow chart of the known MCHES process, the return of the mother liquor during the chlorination phase leads to the accumulation of DCHES (dichloroacetic acid) in the model, which necessitates the discharge of a portion of the mother liquor to be destroyed. Furthermore, the high concentration of DCHES also reduces the yield of the crystallization stage.
One disadvantage of the known MCHES process is that a portion of the mother liquor has to be destroyed, which leads to a high raw material consumption index and a reduced capacity in the crystallization stage due to the high content of DCHES in the monochloroacetic acid blank.
The object of the present invention is to reduce the raw material consumption index and to improve the productivity in the crystallization of MCHES.
The object is achieved by introducing a hydrogenolysis stage of the MCHES blank after the chlorination stage and by further feeding the product to the crystallization stage after the chlorination stage.
Figure 2 shows a flow diagram of the proposed monochloroacetic acid process.
The results obtained, consisting of a reduction in the index of consumption of raw materials and an increase in the capacity of the crystallization stage, are guaranteed by the following measures: the catalytic hydrogenolysis stage, which introduces the MCHES feedstock after the chlorination stage, reduces the amount of DCHES in the feedstock from 7% by weight to 1-1.5% by weight, eliminating the need for spent mother liquor, i.e., the accumulation of DCHES in the model.
Furthermore, reducing the content of DCHES in the MCHES billet leads to an increase in the productivity of the crystallization stage, all other things being equal.
Fig. 2 shows a block diagram of the proposed method for the preparation of MCHES. The results obtained, which reduce the consumption of raw materials and increase the capacity of the crystallization stage, are ensured by introducing a subsequent step of catalytic hydrogenolysis of the MCHES intermediate product after the chlorination step, and by reducing the amount of DCHES in the intermediate step by 7% by weight by 1-2.5% by weight. Thus, it is no longer necessary to vent mother liquor destruction (accumulation of DCHES is excluded in the block flow diagram). Furthermore, reducing the DCHES content of the MCHES intermediate product leads to an increase in the capacity of the crystallization stage, all other things being equal.
As the catalyst, 0.5 to 2% by weight of palladium-supported activated carbon was used.
(substitution hydrogenation)
The proposed solution is explained in detail below with examples.
Example 1 (known Process)
The catalytic chlorination of acetic acid (addition of 33.6g/n acetic anhydride) was carried out in a jacketed reactor (column) at a temperature of 110 ℃ in the liquid phase with gaseous chlorine. The chlorination is carried out with a 10 mole% excess of chlorine.
The crystallization stage is a volumetric apparatus with a jacket through which a coolant is passed. The MCHES billet is cooled in the crystallizer from 50 ℃ to 20 ℃ over 12 hours.
After the crystallization process, the suspension obtained is sent to centrifugation. Thereafter the mass and composition of the mother liquor and the amount and composition of commercially available MCHES were determined.
From the test results, the index of consumption of the starting material and the yield of the desired product at the crystallization stage can be obtained.
The conditions under which the tests were carried out and the results obtained are listed in the table.
Example 2
The chlorination of acetic acid was carried out analogously to the process described in example 1.
The MCHES blank obtained in chlorination is sent to the catalytic hydrogenolysis stage. The process is as followsIn a volumetric apparatus containing 40g of an activated carbon catalyst loaded with 1% by weight of palladium at a temperature of 140 ℃ DCHES: H2The molar ratio is 1: 7.
After the hydrogenolysis stage the product is sent to the crystallization stage. The crystallization was carried out analogously as described in example 1.
From the test results, the index of consumption of the starting material and the yield of the desired product in the crystallization stage were obtained.
The conditions under which the tests were carried out and the results obtained are listed in the table.
The data listed in the analysis table show that the use of a hydrogenolysis process on the MCHES feedstock after the chlorination stage greatly reduces the consumption index of the raw materials acetic acid and chlorine and improves the productivity of the crystallization stage.
An important distinguishing feature of the proposed monochloroacetic acid process is the use of a catalytic hydrogenolysis stage in the MCHES feedstock between the chlorination and crystallization stages.
Watch (A)
Example 1 example 2 Chlorination phase addition of CL2g/h 331.76331.76 adding ES (acetic acid) g/h 235.85235.85 to obtain MCHES blank g/h 396.00396.00
MCHES 297.00 297.00
DCHES 27.72 27.72
Hydrogenolysis products of an ES 71.2871.28 hydrogenolysis stage, g/h 390.03, wherein, g/h
MCHES 313.35
DCHES 5.40
Raw material for crystallization in ES 71.28 crystallization stage, g/operation 396.0390.03 wherein g/operation
MCHES 297.00 313.25
DCHES 27.72 5.40
ES 71.2871.28 yields: mother liquor g/run 196.00149.24 wherein g/run
MCHES 99.00 74.56
DCHES 26.72 4.40
ES 70.2870.28 commercial MCHES, g/run 200.00240.79 wherein g/run MCHES 198.00238.39 DCHES 1.001.20 ES 1.001.20 consumption index ton 1/tonMCHES acetate 1.180.98 chloride 1.661.38 crystallization ability, g/run 200.00240.79
The disadvantage of this process is the high consumption of supported palladium catalyst (1.5 kg of catalyst per 1 ton of product) and the consequent contamination of the purified MCHES and the low selectivity of the process. Such high consumption of the activated carbon catalyst loaded with 2% by weight of palladium can be explained by the loss of the catalyst in the hydrogen bubbling reactor: the catalyst is captured by the gas stream, lost by mutual friction between the catalyst particles and thereafter carried away by the reaction mixture during the reaction. The reason why the process selectivity is low can be explained as: upon hydrogenolysis according to known methods, not only DCHES but also MCHES are regenerated:
the object of the present invention is to reduce the catalyst consumption and to increase the process selectivity in the purification of MCHES by hydrogenolysis.
The object is achieved by carrying out the hydrogenolysis process in a plant provided with a gas lift. The gas lift is a tube having a hydrogen inlet at the lower portion thereof and is a mixer in which a gas-liquid mixture of hydrogen and MCHES is formed. Due to the low specific gravity of the gas-liquid mixture, it rises up the tube and carries away MCHES from the lower part of the reactor. The separation of the gas-liquid mixture takes place at the outlet of the tube. Wherein hydrogen not participating in the reaction is discharged from the reactor together with the off-gas, and the MCHES is returned to the upper part of the reactor. The reactor was loaded with a hydrogenolysis catalyst between the upper and lower portions of the hydrogen inlet pipe (airlift). The effect generated by the air lifter ensures that the reaction materials circularly move from top to bottom in the volume of the reactor; as a result of which the catalyst layer is pressed by the reaction stream into a support grid. The hydrogenolysis process is carried out by consuming the hydrogen dissolved into the reaction mixture as it passes through the air lift. For a better understanding of the proposed solution described above, see figure 3 for a schematic representation of the hydrogenolysis reactor principle for MCHES.
By excluding the hydrogen inlet from the catalyst layer, positive effects are achieved, namely, reduced catalyst consumption and improved selectivity.
The proposed solution is illustrated by the following examples.
Example 1.
A reactor having a capacity of 150ml was charged with 30g of an activated carbon catalyst loaded with 1% by weight of palladium and 120g of a MCHES billet containing 8.6% by weight of DCHES. After heating the reaction mass to 140 ℃ hydrogen was added at a rate of 6L/h.
After 6 hours, hydrogen supply was stopped. The DCHES content of the reactants was as low as 1.18% by weight and the acetic acid content was 2.8% by weight, consuming 1.5g of catalyst per 1kg of reaction mixture.
Example 2.
A reactor having a capacity of 150ml was charged with 30g of an activated carbon catalyst loaded with 1% by weight of palladium and 120g of a MCHES billet containing 8.6% by weight of DCHES. After heating the reaction mixture to 140 ℃ hydrogen was added at a rate of 9L/h.
Hydrogenation was stopped after 6 small amounts. The DCHES content of the reaction mixture was reduced to 1.08% by weight, the acetic acid content was 3.7% by weight and the catalyst consumption was 1.65g per 1kg of reaction mixture.
Example 3
A reactor having a capacity of 150ml was charged with 30g of an activated carbon catalyst loaded with 1% by weight of palladium and 120g of a MCHES billet containing 8.6% by weight of DCHES. After the reactants had been heated to 140 c, hydrogen was supplied at a rate of 6l/h to an airlift system, which was a tube (similar to that described above) passing through the catalyst layer.
After 6 hours, the hydrogen supply was stopped. The DHCES content of the reaction mass was reduced to 1.02% by weight, the acetic acid content was 1.56% by weight and the catalyst consumption was 0.05g per 1kg of reaction mixture.
Example 4
A reactor having a capacity of 150ml was charged with 45g of an activated carbon catalyst loaded with 1% by weight of palladium and 120g of a MCHES billet containing 8.6% by weight of DCHES. After heating the reaction mixture to 140 ℃ hydrogen was supplied to the airlift system at a rate of 6 l/h.
After 6 hours, hydrogen supply was stopped. The DCHES content of the reactants was reduced to 0.95% by weight, the acetic acid content was 1.64% by weight and the catalyst consumption was 0.4g per 1kg of reaction mixture.
Example 5
Into a reactor having a capacity of 150lm were charged 45g of an activated carbon catalyst loaded with 1% by weight of palladium and 120g of a MCHES billet containing 8.6% by weight of DCHES. After heating the reactants to 140 ℃ hydrogen was supplied to the airlift system at a rate of 9 l/h.
After 6 hours, hydrogen supply was stopped. The DCHES content of the reactants was reduced to 0.92% by weight, the acetic acid content was 1.62% by weight and the catalyst consumption was 0.05g per 1kg of reaction mixture.
An important special feature of the proposed method is that the method is carried out with an airlift and that all the hydrogen required is fed into the airlift. The result of using an airlift is that the addition of hydrogen is excluded from the catalyst zone, which avoids attrition of the catalyst and reduces its consumption, and improves the quality of the finished product. In addition, the process selectivity is also improved: a relatively small amount of MCHES becomes acetic acid.
The above examples show that the proposed method for purifying MCHES can significantly reduce the consumption of the catalyst containing noble metal palladium, improve the product quality by reducing the catalyst particles and finally improve the product selectivity while maintaining a highly purified product free of DCHES.
In order to use an airlift, the hydrogenolysis process can also be carried out in a membrane-type operation in a unit with a fixed bed catalyst, the catalyst layer being sprayed with a MCHES blank and hydrogen being fed into the upper part of the unit. It is assumed here that the rate of addition of the mentioned MCHES billet must be 4.9X 10-2-1.24m/s。
The process flow diagram of the method is shown below. Please refer to fig. 4
The positive effect of the proposed process is to reduce the catalyst consumption, which can be achieved by carrying out the process for purifying MCHES from DCHES (dichloroacetic acid) impurities in a plant operating in membrane mode, the structure of which is similar to that of a fractionation plant containing packing materials; a palladium-supported catalyst, such as activated carbon loaded with 1% palladium, is used as a filler. This also facilitates the supply of hydrogen into the upper part of the apparatus. This addition of reactants avoids movement of the catalyst particles and thus abrasion and damage thereof.
Assume at 4.9X 10-2The necessity of carrying out the MCHES purification process at a feed rate of-1.24 m/s is that the feed rate is less than 4.9X 10-2m/s, there is a portion of the catalyst on which there is no flow of the MCHES membrane, and thus a vigorous gas phase hydrogenolysis of MCHES to acetic acid occurs on these catalysts, i.e., the selectivity of the process is reduced.
If the process is carried out at a MCHES velocity of more than 1.24m/s, convective flows are formed over the catalyst surface, with the result that the purity of the crude product is reduced.
The invention proposed is illustrated by the following examples.
Example 1 (known method)
A vertical cylindrical apparatus was charged with 80g of an activated carbon catalyst loaded with 1% by weight of palladium and 332g (210ml) of MCHES blank containing 8.6% by weight of DCHES. After heating the reaction to 140 ℃ hydrogen was supplied at a rate of 6 l/h.
After 6 hours, hydrogen supply was stopped. The DCHES content of the reactants was reduced to 1.18% by weight, the acetic acid (ES) content was 2.8% by weight, and the catalyst consumption was 1.5g per 1kg of the reaction mixture.
Example 2
80g of an activated carbon catalyst loaded with 1% by weight of palladium was charged into a vertical cylindrical reactor having a variable diameter, and a blank of MCHES containing 8.6% by weight of DCHES was uniformly distributed in the upper reactor part at a rate of 35ml/h, while hydrogen was supplied at a rate of 6.6L/h. The process was carried out at 140 ℃.
The conditions under which the tests were carried out and the results obtained are shown in the table.
Watch (A)
Test number diameter, cm MCHES feed content wt% catalyst
Speed, m/s DCHES ES consumption, g, example 1- -prototype- -1.182.801.5 example 210.54.954.270.220.020.752.222.410.360.031.01.241.160.470.042.00.310.820.520.053.00.140.610.560.064.00.0780.751.410.075.00.0490.622.000.086.00.0350.593.400.097.00.0290.614.280.0
As can be seen from the data presented in the table, no palladium catalyst is consumed over the listed MCHES feed rate range. The object of the invention of reducing the catalyst consumption is thus achieved.
At a MCHES feed rate of 4.9X 10-2By 1.24m/s, the concentration of DCHES and acetic acid is lower than in the known process.
At velocities above 1.24m/s, the DCHES concentration is higher than known methods; at velocities below 0.049m/s, the acetic acid concentration is higher than in the known process.
As a result, the feed rate of the MCHES billet was 4.9X 10-2In the range of-1.24 m/s, the goal of the invention of improving the selectivity of the process is achieved.
An important feature of the proposed (provided) MCHES purification process is the implementation of the hydrogenolysis process in a unit with fixed bed catalyst in membrane mode operationThe process conditions were to spray the catalyst layer with the MCHES ingot and to supply hydrogen gas at the top of the apparatus. Wherein the feed rate of the MCHES blank is 4.9 x 10-2-1.24m/s。
Claims (7)
1. Process for the preparation of monochloroacetic acid (MCHES) by chlorination of acetic acid, in which a crude MCHES product is produced from which MCHES is separated by crystallization and centrifugation, characterized in that a catalytic hydrogenolysis is carried out before the crystallization.
2. A process as claimed in claim 1, wherein the molar ratio DCHES: H is adjusted during the hydrogenolysis2＝1∶7。
3. A process according to claim 2, characterized in that palladium-loaded activated carbon is used as catalyst, especially activated carbon having a palladium concentration of 0.5 to 2% by weight.
4. A process according to claim 3, wherein the hydrogenolysis is carried out at a temperature of from 125 to 140 ℃.
5. A process according to any one of claims 1 to 4, characterized in that the hydrogenolysis is carried out in an airlift.
6. A process according to any one of claims 1 to 4, characterized in that the hydrogenolysis is carried out in a fixed bed catalyst operated in membrane mode.
7. A process as claimed in claim 6, wherein the crude MCHES is supplied at a rate of from 0.05 to 1.24 m/s.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN94112764A CN1066431C (en) | 1994-12-05 | 1994-12-05 | Preparation of monochloro acetic acid |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN94112764A CN1066431C (en) | 1994-12-05 | 1994-12-05 | Preparation of monochloro acetic acid |
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| Publication Number | Publication Date |
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| CN1124243A true CN1124243A (en) | 1996-06-12 |
| CN1066431C CN1066431C (en) | 2001-05-30 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN94112764A Expired - Fee Related CN1066431C (en) | 1994-12-05 | 1994-12-05 | Preparation of monochloro acetic acid |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102001930A (en) * | 2010-10-15 | 2011-04-06 | 中国天辰工程有限公司 | Method for purifying chloroacetic acid by catalytic hydrogenolysis in chloroacetic acid production and application thereof |
| CN104326897A (en) * | 2014-11-21 | 2015-02-04 | 河北科技大学 | Continuous crystallization method of chloroacetic acid |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1027889C (en) * | 1991-01-31 | 1995-03-15 | 翟超进 | Method for preparing monochloro-acetic acid |
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1994
- 1994-12-05 CN CN94112764A patent/CN1066431C/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102001930A (en) * | 2010-10-15 | 2011-04-06 | 中国天辰工程有限公司 | Method for purifying chloroacetic acid by catalytic hydrogenolysis in chloroacetic acid production and application thereof |
| CN102001930B (en) * | 2010-10-15 | 2014-08-27 | 中国天辰工程有限公司 | Method for purifying chloroacetic acid by catalytic hydrogenolysis in chloroacetic acid production and application thereof |
| CN104326897A (en) * | 2014-11-21 | 2015-02-04 | 河北科技大学 | Continuous crystallization method of chloroacetic acid |
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| CN1066431C (en) | 2001-05-30 |
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